The present application claims priority to Japanese Application No. P2000-048962 filed Feb. 21, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to an optical recording medium, an optical pickup for exposing the converged light to the optical recording medium, and an optical recording and/or reproducing apparatus for recording and/or reproducing an signal by exposing the converged light to the optical recording medium.
2. Description of the Related Art
As examples of the optical apparatus, there is known an optical recording and/or reproducing apparatus for recording and/or reproducing of the information using an optical recording medium such as an optical disk and an optical microscope.
The cut-off spatial frequency fc in the optical apparatus is generally expressed by the following equation (1) using the numerical aperture NA of the objective lens and the wavelength xcex of the output light from the light source.
fc=2NA/xcexxe2x80x83xe2x80x83(1)
The higher density recording is attempted in the optical recording and/or reproducing apparatus and the more detailed observation can be done in the optical microscope, the shorter the wavelength xcex of the light from the light source becomes, further the larger the numerical aperture NA of the objective lens becomes.
As a method for making the numerical aperture NA of the objective lens larger, the near field optical system using a solid immersion lens (SIL) is known, and the optical system which the numerical aperture is greater than 1 is realized by this method.
As a paper describing the near field optical system and solid immersion lens, for example, a paper of S. M. Mansfield, W. R. Studenmund, G. S. Kino, and K. Osato, xe2x80x9cHigh-numerical-aperture lens system for optical storagexe2x80x9d, Opt. Lett. 18, pp.305-307 (1993) is known.
Further, as another paper, for example, a paper of H. J. Mamin, B. D. Terris, and D. Rugar, xe2x80x9cNear-field optical data storagexe2x80x9d, Appl. Phys. Lett. 68, pp.141-143 (1996) is known.
Note that, the U.S. Pat. No. 4,183,060 and the U.S. Pat. No. 4,300,226 discloses the detection of distance between the optical disk and the electrode by an electrostatic capacitor sensor, however, descriptions about the near field optical system or the solid immersion lens (SIL) are not disclosed.
Japanese Unexamined Patent Publicaion (Kokai) No.H8-212579 discloses an optical head and a recording medium driving apparatus are disclosed. In this Publication, it is disclosed that the objective lens is held by the first lens holder, the immersion lens is held by the second lens holder, the conductive member are used for the second lens holder, and the position control of the immersion lens is carried out based on the electrostatic capacitor between the second lens holder and the optical disk.
When any signal is recorded optically on the optical recording medium or when the recorded signal is reproduced, while the numerical aperture NA of the optical system is large, a coupling of the luminous flux to the optical recording medium is important and relates to the forming of the light spot at the recording layer in the optical recording medium closely.
An object of the present invention is to provide an optical recording medium capable of improving the contribution of the converged light to the forming of the light spot when the converged light from the optical system forms the light spot at the recording layer in the optical recording medium.
Another object of the present invention is to provide an optical pickup capable of improving the contribution of the converged light to the forming of the light spot when the converged light from the optical system forms the light spot at the recording layer in the optical recording medium.
Still another object of the present invention is to provide an optical recording and/or reproducing apparatus capable of improving the contribution of the converged light to the forming of the light spot when the converged light from the optical system forms the light spot at the recording layer in the optical recording medium.
According to the present invention, there is provided an optical recording medium to which light for recording and/or reproducing a signal is emitted, comprising one or a plurality of inorganic deelectric layers provided at an incident side to which the light is converged, and an amplitude transmittance, which is a ratio of the light reached to a recording layer in the optical recording medium to the converged light passed through outer circumference area of an objective lens, being equal or greater than 30%.
Specifically, the objective lens comprises a solid immersion lens having a large numerical aperture to form a near field.
Preferably, a refractive index of the outermost layer among the inorganic deelectric layers is equal or greater than the refractive index of the objective lens.
Further preferably, an optical recording medium according to the present invention further comprises a first and a second deelectric layers, and the recording layer is positioned between the first and the second deelectric layers, and the first deelectric layer is positioned between the inorganic deelectric layer and the recording layer.
Specifically, the inorganic deelectric layer is a single layer of silicon nitride (SiN).
According to the present invention, there is also provided an optical pickup, comprising a light source, an optical system for converging light from the light source and emitting the converged light to an optical recording medium, and a photodetector for outputting an output signal in response to light reflected at the optical recording medium and passed through the optical system, and the optical recording medium comprising one or a plurality of inorganic deelectric layers provided at an incident side to which the converged light from the optical system is emitted, and a refractive index of the outermost layer among the inorganic deelectric layers is equal or greater than the refractive index of the optical system, and an amplitude transmittance, which is a ratio of the light reached to a recording layer in the optical recording medium to the converged light from the optical system passed through outer circumference area of the optical system, being equal or greater than 30%.
Preferably, the optical system comprises; an objective lens for converging the light emitted from the light source, and a solid immersion lens having a large numerical aperture to form a near field for converging the light passed through the objective lens and emitting the light to the optical recording medium, and the refractive index of the outermost layer among the inorganic deelectric layers is equal or greater than the refractive index of the solid immersion lens.
Specifically, the light source is a laser for outputting a blue or a blue purple laser beam, and the optical system is a near field optical system.
According to the present invention, there is further provided an optical recording and/or reproducing apparatus, comprising a light source, an optical system for converging the light from the light source and emitting the converged light to an optical recording medium, a photodetector for generating an output signal in response to light reflected at the optical recording medium and passed through the optical system, a modulation circuit for modulating the intensity of the light from the light source in response to the recording signal to the optical recording medium, and a detection circuit for detecting the signal recorded on the optical recording medium in response to the output signal from the photodetector, and the optical recording medium comprising one or a plurality of inorganic deelectric layers provided at an incident side to which the converged light from the light system is emitted, and a refractive index of the outermost layer among the inorganic deelectric layers is equal or greater than the refractive index of the optical system, an amplitude transmittance, which is a ratio of the light reached to a recording layer in the optical recording medium to the converged light from the optical system passed through the outer circumference area of the optical system, being equal or greater than 30%.
Preferably, the optical system comprises an objective lens for converging the light emitted from the light source, and a solid immersion lens having a large numerical aperture to form a near field for converging the light passed through the objective lens and emitting the light to the optical recording medium, and the refractive index of the outermost layer among the inorganic deelectric layers is equal or greater than the refractive index of the solid immersion lens.
Specifically, the light source is a laser for outputting a blue or a blue purple laser beam, the optical system is a near field optical system.
By making an amplitude transmittance, which is a ratio of the light reached to a recording layer in the optical recording medium to the converged light passed through the outer circumference area of the optical system, 30% or more or about 30% or more, the contribution of the converged light to forming of the light spot is improved and it is capable to realize the optical recording medium capable of high density recording.